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The outcome and morbidity in these cases is determined by the pathology and anatomical
position of the epileptogenic zone. The extent of the resection may also influence the
neuropsychological sequelae of a resection, but in many cases is predictable.

Hemispherectomy
Hemispherectomy was first described in the management of malignant cerebral tumours. This
established the surgical technique but quickly demonstrated that the indications were
inappropriate. In 1938 McKenzie described the application of the procedure in a patient with
medically intractable seizures and behavioural problems. Over the next 25 years the
procedure was widely used in patients with intractable seizures. The inevitable consequence
of a hemispherectomy is a profound neurological deficit, including hemiplegia and
hemianopia, however many of the patients considered for surgery already have these
neurological deficits. In the 1960s the original anatomical procedure fell into disrepute as the
procedure caused long-term complications in many patients such as hydrocephalus, and in
some cases resulted in death.

As a result alternative techniques for either obliteration of the surgical cavity or disconnection
of the hemisphere were developed. First, Rasmussen described a functional hemispherectomy
in which the temporal lobe and central cortex were removed and the corpus callosum and
frontal and occipital cortex disconnected. This procedure was subsequently made less
invasive by Delalande and Villemure who described different techniques of
hemispherectomy. The consensus view of these alternative techniques is that, when properly
performed, the outcomes are very similar if disconnection and not resection is performed.

The success of hemispherectomy depends on the underlying pathology, with excellent
outcomes expected for pathologies such as Rasmussen’s encephalitis and focal infarcts, and
a poorer outcome expected in patients with hemi-megalencephaly.

Functional procedures

The objective in functional epilepsy surgery is to palliate rather than to cure the epilepsy.
Functional procedures should only be considered once resective surgery has been deemed
inappropriate, or to carry too great a risk.

Corpus callosotomy
Corpus callosotomy was first developed in the 1940s following the observation that in
patients undergoing transcallosal exploration of tumours, seizures were reduced in frequency.
The primary indication for corpus callosotomy is atonic drop attacks, although it has been
used to good effect in other epilepsy types and syndromes. The major concern with corpus
callosotomy is the risk of either immediate or delayed symptoms of disconnection. In order
to prevent or minimise the risk of a disconnection syndrome the callosotomy should be
carried out in two stages, with the anterior two-thirds of the corpus callosum being divided
at the first operation and the posterior third divided if and when the callosal section is
completed. In children under the age of 12 years there is no evidence to suggest that long-
term disconnection syndrome occurs and for this reason a one-stage complete callosotomy is
carried out whenever possible in this younger age group.

Careful surgical technique is essential for this procedure and great attention needs to be paid
to preservation of the vascular anatomy, particularly the bridging veins, and retraction should,
as always, be kept to the minimum.